Off-highway vehicles (OHV) increasingly rely on electronically controlled, safety-critical systems such as braking, steering, powertrain, and implement control electronic control unit (ECUs). The integration of connectivity, telematics, precision-agriculture features, and semi-autonomous operation has transformed these machines into complex cyber-physical systems. While these capabilities improve productivity and operational efficiency, they also expand the attack surface, creating cybersecurity risks that can directly impact vehicle control, operator safety, and field operations. Off-highway platforms often operate in remote environments, use legacy in-vehicle networks, and have long service lifecycles, further amplifying exposure to cyber threats. Recent research and real-world demonstrations highlight that many attacks on safety-critical controllers exploit fundamental architectural weaknesses rather than advanced exploits. Common scenarios include unauthenticated CAN-based communication enabling message injection, replay, or spoofing of steering and braking commands; compromised telematics or wireless interfaces pivoting into safety-critical networks; unsecure over-the-air update mechanisms permitting unauthorized firmware installation; and misuse of diagnostic or maintenance access paths to invoke privileged ECU functions. Network-level attacks such as denial-of-service and sensor-level manipulation, including GPS or perception spoofing, further threaten the integrity and availability of control functions relied upon by modern agricultural machines. This paper examines these attack scenarios in the context of off-highway safety-critical controllers and discusses how Hardware Security Modules (HSMs) provide a practical trust anchor for mitigating such risks. HSMs onboard hardware-isolated execution, tamper-resistant key storage, and cryptographic enforcement that strengthen ECU security beyond secure boot. HSM-backed mechanisms enable authenticated and integrity-protected software updates, prevent execution of unauthorized firmware, support message authentication and freshness on in-vehicle networks, and harden diagnostic access through secure challenge-response mechanisms. By grounding cybersecurity risks in realistic off-highway use cases and mapping them to deployable HSM-backed controls, the paper illustrates how hardware-anchored security enhances runtime trust, supports safety objectives, and aligns off-highway vehicle architectures with emerging vehicle cybersecurity expectations, including the EU Cyber Resilience Act (CRA). In addition, a PoC implementation based on an automotive-grade embedded controller is presented to demonstrate secure boot, authenticated CAN communication, diagnostic access control, and runtime integrity monitoring, together with a validation methodology that demonstrates their practical effectiveness.